It's unlikely that the lump in your breast is cancerous.However it's really not very wise of you to have had this lump in your breast for over 3 years without having it checked out by a medical professional who could have ordered an Ultrasound and maybe more tests (if needed) and put your mind at ease.
This lump could very well be a fibroadenoma (benign growth) but I urge you to see your doctor for evaluation,since no one can tell you for sure what it could be.
Please make that phone call to your doctor soon.Your health is much more important than what your family may or may not feel anxious about this problem.
Take care and I wish you well...
Were it cancer it would have grown in size and you would have other symptoms. It is possible that it is a cyst, I guess. I get cysts all the time and have one just below the surface of my left breast now.